The efficacy of the ten per cent reducior in overcoming the intrferrnce of nickel in the deter-
mmination of UO, volumetrically is verified with a group of -ynthetic mixture The deleterious effect
of copper in ore samples is noted, and the various effect of the presence of copper are investigated.
The satisfactory determination of uranium in nickel bearing ores, provided that copper and reducible
elements other than uranium are removed, is shown.

INTRODUCTION

J. B. Heberling,' in his investigation of the effect uf various contaminants found in ore saniples on
the volumetric determination of uranium, showed that nickel pi vented complete reduction by its injurious
effect on the Jones Reductor On the basis of later work, F S Grnmaldi' has shown that the difficulties
entailed by the poisoning of a Jones Reductor with nickel ran be overcome by using an amalgam richer in
mercury than is usual. By am 3lgamat in the zinc len pi r cent by weight of mercury, he has been able to
pass more than five grams of nickel through the reductor without any poisoning effect The reductor was
not contaminated by the nickel and the uranium was reduced satisfactorily to the trivalent and tetravalent
states.

The following work was done to determine whether or not uranium in ore samples, containing
large amounts of nickel, could be determined accurately with think ten per cent rpductor. It was hoped
that the hydrogen sulfide precipitation could be dispensed with, but difficulties were encountered due
to the presence of copper.

In respect to this, A. R. Nichols2 has shown that cupric chloride catalyzes the autoxidation of
uranous to uranyl ion.

The effect of copper sulfate on the reduction and narration ni uranium was investigated.

Eight solutions were prepared, each containing 0.3750 granm of U,O, and 0 157 gram ol nickel in
75 ml of diluted sulfuric acid (5- 95). The solution. were passed through the ten per cent reductor at
a rate of about 50 ml per minute, waLhed with 100 ml of dilute surfurac acid t5-95), and then with
100 ml of distilled water. The reduced solutions were aerated for fifteen minuirs and titrated with
standard potassium dichromate solution of about 0.027N'. The result; are given in Table 1.

It was confirmed that solutions coiit:iininr uraniumr .nd nri kt cran be passed through the ten per
cent reductor without the usual darkening and gassing effl.:t-: nd with coniplett reduction ol the uranium.

As a means of comparison, several samples of Canadian ore were analyzed using the standard
method as outlined.

1) The samples were decomposed by treating with aqua regia, heated with hydrobromic and hydro-
chloric acids to remove any arsenic, and fumed with sulfuric acid in the presence of nitric acid to
remove any excess hydrobromic acid. After fuming with sulfuric acid to remove the nitric, the samples
were cooled, diluted, and electrolyzed by the mercury cathode method. Subsequently, the solutions, thus
purified of any copper, nickel, and other metals amenable to separation by this means, were further
purified by using the cupferron precipitation and chloroform extraction. The excess organic matter was
destroyed by fuming with nitric acid and with perchloric acid. Any excess nitric acid was removed by
fuming twice with sulfuric acid.

The solutions were then diluted and passed through the usual Jones Reductor, aerated, and titrated
with standard potassium dichromate.

2) As a test of the ten per cent Jones Reductor, several more samples were treated as in Method 1
except that no separation with the mercury cathode was made and reduction was carried out by means of
the ten per cent reductor. The reductor was darkened upon passage of the solutions, and a black residue
was deposited in the glass wool at the bottom of the column and in the solution. Prior to aeration the
color of the solutions changed from dark to light green. This suggested that some contaminant was cat-
alyzing the oxidation of the uranium.

3) Three more samples were treated as in Method I except that a hydrogen sulfide separation was
performed in place of the mercury cathode electrolysis, and reduction was carried out by means of the
ten per cent reductor. No darkening of the reductor was caused by the passage of these samples, and no
black deposit was observed in the glass wool. Prior to aeration, the dark olive green color of the solu-
tions was retained.

The results obtained by these methods are given in Table 2.

The Effect of Copper on the Reduction and Aeration of Uranium

On the assumption that copper was the contaminant present in ore samples responsible for erratic
results, several experiments were carried out to determine the effect of this element.

Solutions containing 0.3750 g of UO, and 0.050 g of copper were reduced in the Jones Reductor,
aerated for 15 minutes, and litrated with standard (0.027N) potassium dichromale. These samples
titrated low.

Solutions containing 0.370 g of U3Oe and copper in varying amounts were passed through the re-
ductor and caught in 20 ml of 4%c.ierric chloride. Without aeration these solutions were titrated with
0.027N potassium dichromate. The U,30 found was in slight excess of the amount added indicating
that some trivalent uranium or reduced copper was titrated However, since the excess was at least
as great with 5 mg of copper as with 50 mg of copper, it appears that uranium was completely reduced
to quadrivalent state.

Approximately 0.375 g portions of U.O in sulfuric acid solution were reduced in the Jones Reductor
and added to a solution of copper sulfate. Immediately a (ine, light precipitate, purplish in color, formed.
Upon aeration this precipitate redissolved. The samples titrated low.

Two more portions of UsOe in sulfuric acid solution were reduced in the Jones Reductor, aerated
for fifteen minutes, added to a copper sulfate solution, and aerated again. No precipitate of metallic
copper was formed but the results were low. Data for these investigations are given in Table 3.

It was found that copper has a harmful effect on the Jones Reductor and on the aeration of uranium.
This was true of both the ten per cent and the standard reductor. It was determined that copper is
reduced to the metallic state in the presence oi trivalent but not quadrivalent uranium. Copper acts as
a catalyst in the oxidation by aeration of quadrivalent uranium to the hexavalent state.

CONCLUSIONS

A Jones Reductor made up of zinc amalgamated with ten per cent by weight of mercury, as outlined
by F. S. Grimaldi,2 will prove satisfactory for the determination of uranium in nickel bearing ore sam-
ples provided that other elements reduced by the reductor and any elements such as copper, catalyzing
the autoxidation of uranium, are removed before reduction.

If copper is present in the sample to be reduced, it will catalyze the oxidation of the quadrivalent
to hexavalent uranium during the aeration. Copper is reduced to the metallic state in the reductor, but
is not completely retained in the column.

MDDC 901

Table 3. Effect of copper on the reduction and aeration of uranium solutions.